Continuous Pump Station Performance Evaluation Using Established Flow Monitoring Equipment

The City of Suffolk, Virginia (City) entered into a Special Order by Consent (SOBC) with the Virginia Department of Environmental Quality (DEQ), the Hampton Roads Sanitation District (HRSD), and other area localities to reduce sanitary sewer overflows (SSOs) from wastewater collection systems. As part of the SOBC, the City was required to develop and conduct a flow monitoring program to determine which service areas exhibit excessive infiltration and inflow (I/I). Service areas found to have excessive I/I were required to undergo a sanitary sewer evaluation survey (SSES) and subsequent rehabilitation.The City was limited in their ability to retrofit flow monitors on their existing stations primarily because of the space and access restrictions on the discharge piping. As a result, an alternative approach was deployed in which the pump station’s flow is calculated using a flow algorithm that combines dynamic data from pressure sensors at hydraulically important locations in the station with key static data such as the station’s wet well and sewer system dimensions and elevations. A key component of the flow calculation is a field generated pump curve (station operating curve).The flow monitoring equipment installed in over ninety (90) pump stations is now being used to continually evaluate pump station performance, leading to a decrease in performance related SSOs. The station operating curves, developed to support the flow monitoring, are compared with manufacturer provided pump curves and evaluated for significant differences. Differences between the operating curve and factory curve are often indicative of certain operational issues (e.g., debris lodged in check valves, partially closed system valves, pump seating issues, etc.). Each issue has a specific effect on the operating curve shape.Currently, all pump stations within the City of Suffolk are undergoing continuous performance evaluation. Pump station operating curves are being developed at least once a year as a routine O&M activity. Additionally, operating curves are redeveloped when a pump is replaced or major maintenance at the pump station is performed. This evaluation process is now part of the City’s Capacity, Management, Operation and Maintenance (CMOM) Program and has brought over 60 underperforming pump stations, or approximately 40% of the City’s pump stations, back to the designed station performance, which reduces the risk of SSOs. To the knowledge of the authors, this type of preventative maintenance is not being performed anywhere else. A sample of the operating curve and factory curve comparison is shown below.